Hops, in the form of either the ground dried plant or an extract, are used in brewing to give the malt beverages, such as beer or ale, their characteristic bitter flavor and pleasant aroma. The hops or a hop extract may be added to boiling wort in the brewing kettle. An isomerized hop extract, if it is highly purified, may be added post kettle, i.e., after the wort has been boiled or after fermentation.
The primary hop constituents used in the brewing process are the alpha acids, the beta acids, the uncharacterized soft resins and the hop oils. The alpha acids are known as humulones and the beta acids are known as lupulones. The alpha acids are the precursors of the bitter substances in beer. The beta acids or lupulones have low solubility in kettle wort and beer and play a relatively minor role in the brewing process.
During brewing, chemical changes are made in the humulones resulting in the formation of compounds known as isohumulones, i.e., isohumulone, isocohumulone and isoadhumulone. These iso-alpha acids are formed in the kettle during the boiling stage of the normal brewing process and are the primary contributors to the characteristic bitter flavor of beer and ale.
Hop extracts have been used in brewing beer for a number of years. The reasons are several fold. When whole hops are added to the kettle, the yield of isohumulone is poor, e.g., 20-25% based on the humulone present in the hops. However, the conversion of humulones in a hop extract to isohumulones can be very high, e.g. 80%. Furthermore, the utilization of the pure isohumulones in a preisomerized extract which is added post kettle is known to be extremely high, e.g. 70-90%.
In order to use a hop extract post kettle, it must contain isohumulones of a high degree of purity and only insignificant amounts of the other components of a preisomerized extract such as lupulones, waxes and other hop insoluble residues which can cause substantial haze, i.e., turbidity or gushing, i.e., rapid carbon dioxide release.
Extracts containing isohumulones of only 80% purity, for example, cannot be added post kettle in amounts exceeding approximately 10-15 p.p.m. of isohumulone without the possibility of causing turbidity in the finished product. On the other hand, extracts containing isohumulone of high purity, 90%+, can be added post kettle at levels exceeding 20 p.p.m. without a significant increase in turbidity.
It is known that isohumulone derived from hops or an unreduced hop extract can cause light instability in malt beverages. The exposure of such a beer or ale to light can result in the beverage becoming "light struck" and having a skunky odor.
The present invention relates to hopping materials, including hop extracts, which may be used to prepare light stable or anactinic malt beverages and to methods of preparing such materials without using organic solvents.
The prior art practice for the production of anactinic hopping materials consists of extracting the essential bittering acids from the cellulosic material of the hop blossom by the use of either organic solvents (e.g., alcohols, chlorinated hydrocarbons, low boiling petroleum solvent) or carbon dioxide, separating the solvent phase from the solid phase, and chemically processing the solvent phase which contains the extracted hop acids to isomerize and reduce the humulones present. The prior art use of organic solvents is now frowned on because of the possibility of residues in the final products and environmental considerations involved in getting rid of organic solvents. These problems are eliminated by CO.sub.2 extraction, but unfortunately it involves the use of expensive equipment. In addition, the prior art practices entail some unavoidable product loss in the extraction processes because some 10% or more of the humulone remains in the cellulosic material which is discarded.